Wenjun Bu

Potential Geographic Distribution of Brown Marmorated Stink Bug Invasion (Halyomorpha halys)

Background The Brown Marmorated Stink Bug (BMSB), Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), native to Asia, is becoming an invasive species with a rapidly expanding range in North America and Europe. In the US, it is a household pest and also caused unprecedented damage to agriculture crops. Exploring its climatic limits and estimating its potential geographic distribution can provide critical information for management strategies. Methodology/Principals We used direct climate comparisons to explore the climatic niche occupied by native and invasive populations of BMSB. Ecological niche modelings based on the native range were used to anticipate the potential distribution of BMSB worldwide. Conversely, niche models based on the introduced range were used to locate the original invasive propagates in Asia. Areas with high invasion potential were identified by two niche modeling algorithms (i.e., Maxent and GARP). Conclusions/Significance Reduced dimensionality of environmental space improves native model transferability in the invade area. Projecting models from invasive population back to native distributional areas offers valuable information on the potential source regions of the invasive populations. Our models anticipated successfully the current disjunct distribution of BMSB in the US. The original propagates are hypothesized to have come from northern Japan or western Korea. High climate suitable areas at risk of invasion include latitudes between 30°–50° including northern Europe, northeastern North America, southern Australia and the North Island of New Zealand. Angola in Africa and Uruguay in South America also showed high climate suitability.

Phylogenetic analysis of the true water bugs (Insecta: Hemiptera: Heteroptera: Nepomorpha): evidence from mitochondrial genomes

BackgroundThe true water bugs are grouped in infraorder Nepomorpha (Insecta: Hemiptera: Heteroptera) and are of great economic importance. The phylogenetic relationships within Nepomorpha and the taxonomic hierarchies of Pleoidea and Aphelocheiroidea are uncertain. Most of the previous studies were based on morphological characters without algorithmic assessment. In the latest study, the molecular markers employed in phylogenetic analyses were partial sequences of 16S rDNA and 18S rDNA with a total length about 1 kb. Up to now, no mitochondrial genome of the true water bugs has been sequenced, which is one of the largest data sets that could be compared across animal taxa. In this study we analyzed the unresolved problems in Nepomorpha using evidence from mitochondrial genomes.ResultsNine mitochondrial genomes of Nepomorpha and five of other hemipterans were sequenced. These mitochondrial genomes contain the commonly found 37 genes without gene rearrangements. Based on the nucleotide sequences of mt-genomes, Pleoidea is not a member of the Nepomorpha and Aphelocheiroidea should be grouped back into Naucoroidea. Phylogenetic relationships among the superfamilies of Nepomorpha were resolved robustly.ConclusionThe mt-genome is an effective data source for resolving intraordinal phylogenetic problems at the superfamily level within Heteroptera. The mitochondrial genomes of the true water bugs are typical insect mt-genomes. Based on the nucleotide sequences of the mt-genomes, we propose the Pleoidea to be a separate heteropteran infraorder. The infraorder Nepomorpha consists of five superfamilies with the relationships (Corixoidea + ((Naucoroidea + Notonectoidea) + (Ochteroidea + Nepoidea))).

18S rRNA hyper-elongation and the phylogeny of Euhemiptera (Insecta: Hemiptera)

The small subunit of nuclear ribosomal RNA (SSU nrRNA), whose sedimentation is mostly 18S in eukaryotes, is considered a relatively conservative marker for resolving phylogenetic relationship at the order level or higher. Length variation in SSU nrDNA is common, and can be rather large in some groups. In studies of Hexapoda phylogeny, the SSU nrDNA has been repeatedly used as a marker. Sternorrhyncha has been rarely included. The lengths of SSU nrDNAs of sternorrhynchids, the basal group of Hemiptera identified in the previous study are 0.3-0.6 kb longer than the usual ones in Hexapoda (1.8-1.9 kb). To use the entire SSU nrDNA sequences or the length-variable parts could cause alignment trouble and therefore affect phylogenetic results, as shown in this study of Euhemiptera phylogeny. Two problems are particularly noticeable. One is that two hyper-variable regions flanking a short length-conservative region could become overlapped in the alignment. This will destroy the positional homology over a larger range. The other is that, when a base pair in a stem of the secondary structure is located near the length-variable regions (LVRs), the simultaneous positional homology of these two bases in the pair is always lost in the alignment results. In this study, the secondary structure model of Hexapoda SSU nrRNA was slightly adjusted and the LVR distributions in it were finely positioned. The noise caused by the hyper LVRs was eliminated and the simultaneous homology for the paired bases was recovered based on the secondary structure model. These corrections improved the quality of the data matrix and hence improved the resolving behavior of the algorithm used. This study provided more convincing evidence for resolving the Euhemiptera suborders phylogeny as (Archaeorrhyncha+(Clypeorrhyncha+(Coleorrhyncha+Heteroptera))). This result provided a more solid background for outgroup determination according to the phylogenetic studies inside each suborder. The problems caused by LVRs have seldom been well addressed. As phylogenetic reconstruction depends more on the data matrix itself than on the algorithm, and length variation of SSU/LSU rRNA exists more or less in any group, it is necessary to closely investigate the effect of rRNA length variation on alignment and phylogenetic reconstruction in more groups.

Higher Level Phylogeny and the First Divergence Time Estimation of Heteroptera (Insecta: Hemiptera) Based on Multiple Genes

Heteroptera, or true bugs, are the largest, morphologically diverse and economically important group of insects with incomplete metamorphosis. However, the phylogenetic relationships within Heteroptera are still in dispute and most of the previous studies were based on morphological characters or with single gene (partial or whole 18S rDNA). Besides, so far, divergence time estimates for Heteroptera totally rely on the fossil record, while no studies have been performed on molecular divergence rates. Here, for the first time, we used maximum parsimony (MP), maximum likelihood (ML) and Bayesian inference (BI) with multiple genes (18S rDNA, 28S rDNA, 16S rDNA and COI) to estimate phylogenetic relationships among the infraorders, and meanwhile, the Penalized Likelihood (r8s) and Bayesian (BEAST) molecular dating methods were employed to estimate divergence time of higher taxa of this suborder. Major results of the present study included: Nepomorpha was placed as the most basal clade in all six trees (MP trees, ML trees and Bayesian trees of nuclear gene data and four-gene combined data, respectively) with full support values. The sister-group relationship of Cimicomorpha and Pentatomomorpha was also strongly supported. Nepomorpha originated in early Triassic and the other six infraorders originated in a very short period of time in middle Triassic. Cimicomorpha and Pentatomomorpha underwent a radiation at family level in Cretaceous, paralleling the proliferation of the flowering plants. Our results indicated that the higher-group radiations within hemimetabolous Heteroptera were simultaneously with those of holometabolous Coleoptera and Diptera which took place in the Triassic. While the aquatic habitat was colonized by Nepomorpha already in the Triassic, the Gerromorpha independently adapted to the semi-aquatic habitat in the Early Jurassic.

A unique box in 28S rRNA is shared by the enigmatic insect order Zoraptera and Dictyoptera.

The position of the Zoraptera remains one of the most challenging and uncertain concerns in ordinal-level phylogenies of the insects. Zoraptera have been viewed as having a close relationship with five different groups of Polyneoptera, or as being allied to the Paraneoptera or even Holometabola. Although rDNAs have been widely used in phylogenetic studies of insects, the application of the complete 28S rDNA are still scattered in only a few orders. In this study, a secondary structure model of the complete 28S rRNAs of insects was reconstructed based on all orders of Insecta. It was found that one length-variable region, D3-4, is particularly distinctive. The length and/or sequence of D3-4 is conservative within each order of Polyneoptera, but it can be divided into two types between the different orders of the supercohort, of which the enigmatic order Zoraptera and Dictyoptera share one type, while the remaining orders of Polyneoptera share the other. Additionally, independent evidence from phylogenetic results support the clade (Zoraptera+Dictyoptera) as well. Thus, the similarity of D3-4 between Zoraptera and Dictyoptera can serve as potentially valuable autapomorphy or synapomorphy in phylogeny reconstruction. The clades of (Plecoptera+Dermaptera) and ((Grylloblattodea+Mantophasmatodea)+(Embiodea+Phasmatodea)) were also recovered in the phylogenetic study. In addition, considering the other studies based on rDNAs, this study reached the highest congruence with previous phylogenetic studies of Holometabola based on nuclear protein coding genes or morphology characters. Future comparative studies of secondary structures across deep divergences and additional taxa are likely to reveal conserved patterns, structures and motifs that can provide support for major phylogenetic lineages.

Influence of data conflict and molecular phylogeny of major clades in Cimicomorphan true bugs (Insecta: Hemiptera: Heteroptera)

Cimicomorpha, which consists of 16 families representing more than 19,400 species, is the largest infraorder in Heteroptera, Insecta. We present the first molecular phylogenetic investigation of family relationships of Cimicomorpha, including 46 taxa from 12 of 16 Cimicomorphan families. Three genes, with a total of 3277 bp of sequence data (nuclear 18S rDNA: 2022 bp, 28S rDNA: 755 bp, and mitochondrial 16S rDNA: 498 bp) were analyzed. Data partitions were analyzed separately and in combination, by employing ML (maximum likelihood), MP (maximum parsimony), and Bayesian methods. As saturation was detected in substitutions of 16S rDNA, influence of data conflict in combined analyses was further explored by three methods: the incongruence length difference (ILD) test, the partitioned Bremer support (PBS), and the partition addition bootstrap alteration approach (PABA). PBS and PABA approaches suggested that 16S rDNA was not very suitable for addressing relationships at this level in Cimicomorpha. Our results also supported the nabid-cimicoid lineage for Cimicoidea proposed by Schuh and Stys [Schuh, R.T., Stys, P., 1991. Phylogenetic analysis of Cimicomorphan family relationships (Heteroptera). J. NY Entomol. Soc. 99 (3), 298-350]. Data incongruence and the utility of the three genes were briefly discussed.

Phylogenomics of Hemiptera (Insecta: Paraneoptera) based on mitochondrial genomes

Hemiptera is the largest order in Paraneoptera and the fifth largest in Insecta. Disputes about hemipteran phylogeny have concerned the monophyly of Auchenorrhyncha and relationships between the suborders Fulgoromorpha, Cicadomorpha, Coleorrhyncha and Heteroptera. In a phylogenomic study of Hemiptera, we add two new mitochondrial genomes of Peloridiidae (Coleorrhyncha) to those reported in GenBank, to complete the taxon sampling of all suborders. We used two types of data – amino acid sequences and nucleotides of various combinations between protein coding genes, tRNAs and rRNAs – to infer the phylogeny of Hemiptera. In total 27 taxa of Paraneoptera were sampled, 24 of them being hemipterans. Bayesian inference, maximum likelihood and maximum parsimony analyses were employed. The relationship of Cicadomorpha + Heteroptera is always stable in the results with different combinations between data types and phylogenetic methods, but our results challenge the monophyly of ‘Homoptera’ and Auchenorrhyncha. In evaluating the relative contribution of each gene, the phylograms generated by single genes CO1, ND1, ND2, ND4 and ND5, respectively, closely matched the tree yielded by the combined datasets. In light of the taxon‐sampling sensitivity of trees based on mitochondrial genomes, the results need to be tested with further data from nuclear genes.

Molecular data and ecological niche modelling reveal the Pleistocene history of a semi‐aquatic bug (Microvelia douglasi douglasi) in East Asia

This study investigated the Pleistocene history of a semi‐aquatic bug, Microvelia douglasi douglasi Scott, 1874 (Hemiptera: Veliidae) in East Asia. We used M. douglasi douglasi as a model species to explore the effects of historical climatic fluctuations on montane semi‐aquatic invertebrate species. Two hypotheses were developed using ecological niche models (ENMs). First, we hypothesized that M. douglasi douglasi persisted in suitable habitats in southern Guizhou, southern Yunnan, Hainan, Taiwan and southeast China during the LIG. After that, the populations expanded (Hypothesis 1). As the spatial prediction in the LGM was significantly larger than in the LIG, we then hypothesized that the population expanded during the LIG to LGM transition (Hypothesis 2). We tested these hypotheses using mitochondrial data (COI+COII) and nuclear data (ITS1 + 5.8S+ITS2). Young lineages, relatively deep splits, lineage differentiation among mountain ranges in central, south and southwest China and high genetic diversities were observed in these suitable habitats. Evidence of mismatch distributions and neutrality tests indicate that a population expansion occurred in the late Pleistocene. The Bayesian skyline plot (BSP) revealed an unusual population expansion that likely happened during the cooling transition between LIG and LGM. The results of genetic data were mostly consistent with the spatial predictions from ENM, a finding that can profoundly improve phylogeographic research. The ecological requirements of M. douglasi douglasi, together with the geographical heterogeneity and climatic fluctuations of Pleistocene in East Asia, could have shaped this unusual demographic history. Our study contributes to our knowledge of semi‐aquatic bug/invertebrate responses to Pleistocene climatic fluctuations in East Asia.

Phylogenetic comparison of local length plasticity of the small subunit of nuclear rDNAs among all Hexapoda orders and the impact of hyper-length-variation on alignment

The SSU nrDNA (18S), is one of the most frequently sequenced molecular markers in phylogenetic studies. However, the length-hyper-variation at multiple positions of this gene can affect the accuracy of alignment greatly and this length variation makes alignment across arthropod orders a serious problem. The analyses of Hexapoda phylogeny is such a case. A more clear recognition of the distribution of the length-variable-regions is needed. In this study, the secondary structure of some length-variable-regions in the SSU nrRNA of Arthropoda was adjusted by the principle of co-variation. It is found that the extent of plasticity of some length-variable-region can extraordinarily be higher than 600 bases in hexapods. And the numbers of hyper length-variable-regions are largest in Strepsiptera and Sternorrhyncha (Hemiptera). Our study shows that some length-variable-regions can serve as synapomorphies for some groups. The phylogenetic comparison also suggested that the expansion of a lateral bulge could be the origin of a helix.

The Complete Mitochondrial Genome of the Stalk-Eyed Bug Chauliops fallax Scott, and the Monophyly of Malcidae (Hemiptera: Heteroptera)

Chauliops fallax Scott, 1874 (Hemiptera: Heteroptera: Malcidae: Chauliopinae) is one of the most destructive insect pests of soybean and rice fields in Asia. Here we sequenced the complete mitochondrial genome of this pest. This genome is 15,739 bp long, with an A+T content of 73.7%, containing 37 typical animal mitochondrial genes and a control region. All genes were arranged in the same order as most of other Heteroptera. A remarkable strand bias was found for all nine protein coding genes (PCGs) encoded by the majority strand were positive AT-skew and negative GC-skew, whereas the reverse were found in the remaining four PCGs encoded by the minority strand and two rRNA genes. The models of secondary structures for the two rRNA genes of sequenced true bugs and Lygaeoidea were predicted. 16S rRNA consisted of six domains (domain III is absent as in other known arthropod mitochondrial genomes) and 45 helices, while three domains and 27 helices for 12S rRNA. The control region consists of five subregions: a microsatellite-like region, a tandem repeats region and other three motifs. The unusual intergenic spacer between tRNA-H and ND4 only found in the species of Lygaeoidea, not in other heteropteran species, may be the synapomorphy of this superfamily. Phylogenetic analyses were carried out based on all the 13 PCGs showed that Chauliopinae was the sister group of Malcinae and the monophyly of Lygaeoidea.